Microcalorimetric and Potentiometric Titration Studies on the Adsorption of Copper by P. putida and B. thuringiensis and Their Composites with Minerals

Abstract

In order to have a better understanding on the interactions of heavy metals with bacteria and minerals in soil and associated environments, isothermal titration calorimetry (ITC), potentiometric titration and equilibrium sorption experiments were conducted to investigate the adsorption behavior of Cu²⁺ by Bacillus thuringiensis, Escherichia coli and their composites with minerals. The adsorption capacity of Cu(II) by bacteriamontmorillonite composite was higher than that by their individual components, whereas bacteria-goethite composite adsorbed less Cu(II) than their individual components. Potentiometric titration revealed that some new adsorption sites were created in bacteria-montmorillonite systems and some adsorption sites were masked in bacteria-goethite systems. The thermodynamic parameters were obtained from the ITC experiments. The negative ΔG values indicated that the adsorptions of Cu(II) by bacteria, minerals and their composites were spontaneous processes. The ΔH values revealed that the reactive sites on bacterial surfaces were more important than those on minerals in binding heavy metals. The positive ΔS values suggested the dominant inner-sphere complexes of Cu(II) on the surface of bacteria, minerals and their composites.